Transcranial magnetic stimulation induction coil device and method of manufacture

ABSTRACT

A transcranial magnetic stimulation induction coil device (“TMS coil device”) is manufactured to contain coil windings of a predetermined size and shape and fixedly positioned at a predetermined location within and orientation in relation to a casing of the TMS coil device. In one embodiment, the coil windings are encased in a casting at a predetermined location within and orientation in relation to the casting, and the casting is fixedly positioned at a predetermined location within and orientation in relation to the casing. The size and shape of the coil windings and the casing within, and the location and orientation of the coil windings in relation to each other and the casing of, the TMS coil device are known with a high level of precision, such that navigated brain stimulation can be performed with the TMS coil device with a high degree of accuracy. In another embodiment, the TMS coil device defines a space interposed between the coil windings and the casing and containing a gas which absorbs heat energy generated at the coil windings, thereby reducing the rate of transfer of heat energy from the coil windings to the casing during operation of the TMS coil device.

CROSS REFERENCE TO RELATED APPLICATION

This application claims the benefit of U.S. Provisional Application No.60/823,991 filed Aug. 30, 2006, assigned to the assignee of thisapplication and incorporated by reference herein.

FIELD OF THE INVENTION

The present invention relates generally to transcranial magneticstimulation and, more particularly, to a transcranial magneticstimulation induction coil device that can be navigated with a highlevel of precision.

BACKGROUND OF THE INVENTION

Transcranial magnetic stimulation (“TMS”) uses an induction coil toinduce an electric field (“E-field”) within the brain. The locations ofthe brain exposed to a strong enough E-field will become activated, orstimulated. In navigated brain stimulation (“NBS”), the E-field inducedin the brain by a TMS induction coil device is graphically representedon a display. As part of NBS, a three-dimensional (“3D”) localizationsystem is used to locate the TMS coil device accurately with respect toa subject's head. The localization system correlates TMS coil devicelocation information with anatomical information representative of asubject's brain, which typically is obtained from magnetic resonanceimaging (“MRI”) of the brain. The E-field information is shown as anoverlay on a graphical display of the subject's brain generated from theMRI images of the brain. By viewing the display, the user caninteractively position the TMS coil device, in real time, in relation tothe brain to stimulate a desired location of the brain.

A TMS induction coil device typically includes coils having 5 to 30loops (windings) of copper wire located in a casing. The windings arenormally circularly shaped or in the form of a FIG. 8. The shape, andthe location of the maximum, of the E-field induced in the brain dependon the exact shape of the coil windings within the TMS coil device andtheir location and orientation with respect to the brain. In NBS, thestrength and location of the E-field induced in the brain by the TMScoil device is determined from information representative of thelocation and orientation of the casing of the TMS coil device inrelation to the brain and the location and orientation of the coilwindings within and in relation to, respectively, the casing. Thelocation and orientation of the casing is obtained from a navigation ortracking device, such as an infrared tracking device including aninfrared transceiver and infrared reflective elements attached to theTMS coil device, that tracks the movement of the casing, as isconventional in the art. The location and orientation of the coilwindings within the casing are determined by generating a model of thecoil windings within the casing of the TMS coil device using informationobtained from, for example, X-ray images of the casing of the TMS coildevice.

It is known that, in NBS, navigation accuracy and the accuracy of thedetermination of the E-field induced in the brain are greatly affectedby any inaccuracies in the model of the coil windings within the casingof the TMS coil device. The manufacturer of a TMS coil device providesinformation on the location and orientation of the coil windings withinthe casing of a TMS coil device, which the manufacturer typicallyobtains by X-raying the casing of the TMS coil device, for use in NBS.The location and orientation information provided by the manufacturercorresponds to the location and orientation in the casing at which thecoil windings are expected to be positioned during manufacture of thecasing.

In presently available TMS coil devices, such as, for example, thosesold by MAGSTIM and MEDTRONIC, however, the coil windings are notnecessarily at the expected location within or orientation in relationto the casing, as indicated by the supplier of the devices, and in somecircumstances, for example, are up to about 10 mm away from the expectedlocation. The difference between the actual and expected locations ofthe coil windings is attributable to manufacturing tolerances relatingto the placement of the coil windings within the casing. Also, thedifference exists because, in the prior art, the coil windingsordinarily are positioned relatively freely within the casing of a TMScoil device. Thus, the coil winding location and orientation informationprovided for current TMS coil devices, which would then be relied uponfor NBS, does not correspond with the actual location and orientation ofthe coil windings within the casing. It has been determined that, wherethe difference between the expected and actual locations of the coilwindings in the casing is up to about 10 mm, inaccuracies in thecomputation of the location and strength of the E-field can be up toabout 10 mm and greater than tenths of a percent, respectively.

In addition, during operation of a TMS coil device, resistive losses inthe copper wire from which the coil windings are formed generate asubstantial amount of heat energy relatively quickly, especially whenthe TMS coil device is operated to supply many sequential pulses to thebrain. The heat energy generated in the coil windings raises thetemperature of the coil windings and also the surrounding casing.Consequently, the temperature of the surface of the casing adjacent orin contact with the head of a subject increases as the heat energy istransferred to the casing. International standards, e.g., IEC-60601-1,require that the temperature of the outer surface of the casing of a TMScoil device should not exceed 41° C., such that the outer surface of thecasing remains at a temperature considered to be safe for contact with asubject, such as a human or animal.

Thus, the temperature of the casing outer surface is a limit on thenumber of times that the TMS coil device can be sequentially pulsed. Thecurrent limitations on the number of pulses that can be sequentiallyapplied by a TMS coil device restricts the potential applications of theTMS coil device, and also lengthens the time that a patient undergoingTMS must endure such procedure, which is undesirable.

In prior art TMS coil devices, the convection techniques of having fluidre-circulate about, or at least partially surround, the coil windingshave been used to increase the rate of transfer of heat energy away fromthe coil windings. In addition, the fluid operates to decrease the rateof transfer of heat energy from the coil windings to the casing, andthus, decrease the rate at which the temperature of the casing outersurface increases. Such uses of fluid to increase the heat capacity ofthe TMS coil device, however, complicate the design and construction ofthe TMS coil device, which must be made waterproof, and alsosubstantially increase the weight of the casing, which makes the TMScoil device more bulky and difficult to maneuver.

Further, in some prior art TMS coil devices, a reduction in the rate ofheat energy transfer from the coil windings to the portion of the casingouter surface that would face or contact the subject's head is achievedbecause the coil windings are positioned a greater distance away fromthe casing portion than in other TMS coil devices. The distance of thecoil windings from the subject's head, however, impacts the maximumE-field that can be induced in the brain. Therefore, it isdisadvantageous for the coil windings to be positioned so far away fromthe casing outer surface portion that the maximum E-field that can beinduced in the brain is undesirably diminished.

Therefore, there exists a need for a TMS coil device that can bemanufactured with ease, repeatedly and inexpensively to provide that thecoil windings are of a predetermined size and shape and are positioned,with great accuracy, at a predetermined location within and orientationin relation to a casing of the TMS coil device having a predeterminedsize and shape and, furthermore, to provide that the rate of transfer ofheat energy from the coil windings to the casing outer surface isminimized without adversely impacting the maximum E-field that can beinduced in the subject's brain.

SUMMARY OF THE INVENTION

In accordance with the present invention, a TMS coil device containscoil windings, preferably made of copper, having a predetermined sizeand shape and which are substantially precisely positioned at apredetermined location within and orientation in relation to a casing ofthe TMS coil device, the casing also having a predetermined size andshape.

In one embodiment of the TMS coil device, each of the coil windings inthe TMS coil device includes inner and outer diameter surfaces and afastener extending between and coupled to the inner and outer diametersurfaces, where the fastener preferably is only on one side of the coilwinding. The fastener substantially fixes the size and shape of the coilwinding.

In another embodiment of the TMS coil device, the coil windings of theTMS coil device, preferably with respective fasteners attached to theinner and outer diameter surfaces, are encased in a casting having apredetermined size and shape and at a predetermined location within andorientation in relation to, respectively, the casting, such that thecoil windings are substantially fixed in location and orientation inrelation to each other and the casing.

In a further embodiment, a casting having a predetermined size and shapeand encasing two coil windings of predetermined size and shape, at apredetermined location within and orientation in relation to thecasting, and preferably with respective fasteners attached to the innerand outer diameter surfaces of the coil windings, can be coupled to acasing of a TMS coil device having a predetermined size and shape, suchthat, when the casting is coupled to the casing, the coil windings aresubstantially fixed at a predetermined location within and orientationin relation to the casing. In a further embodiment, the castingcontaining the encased coil windings includes an aperture for matingwith a projection of the casing, such that, when the projection of thecasing is mated to the aperture of the casting, the coil windings withinthe casting are substantially fixed at a predetermined location withinand orientation in relation to the casing.

In a further embodiment, the casting with the encased coil windings iscoupled to and within the casing, such that a space is definedintermediate at least a portion of the casting and a portion of a bottomwall of the casing whose outer surface will be disposed adjacent or incontact with a subject's head during operation of the TMS coil device.The space includes at least one gas, preferably air, which reduces therate of transfer of heat energy from the coil windings to the bottomwall of the casing.

In another embodiment, the portion of the casing on the side of the coilwindings opposite to the bottom wall of the casing contains a phasetransition material, which absorbs heat energy when transforming fromsolid to liquid and has a low conductivity, such as about 0.1-0.2 W/m*K.The low conductivity of the phase transition material reduces theabsorption of heat energy from the coil windings into the casing. In oneembodiment, the phase transition material is mixed with highconductivity material, such as ceramic, used to form the casing.

BRIEF DESCRIPTION OF THE DRAWINGS

Other objects and advantages of the present invention will be apparentfrom the following detailed description of the presently preferredembodiments, which description should be considered in conjunction withthe accompanying drawings in which like references indicate similarelements and in which:

FIG. 1 is a perspective view of an exemplary TMS coil device inaccordance with the present invention.

FIG. 2A is an exploded, perspective view of an exemplary apparatus formanufacture of a coil winding for a TMS coil device, with the coilwinding as manufactured by the apparatus, in accordance with the presentinvention.

FIG. 2B is partially exploded, perspective view of the apparatus and thecoil winding of FIG. 2A.

FIG. 2C is a perspective view of the apparatus of FIG. 2A at a stepduring manufacture of the coil winding.

FIG. 2D is a plan view of an exemplary guiding disk of the apparatus ofFIG. 2A.

FIGS. 2E and 2F are top and perspective views, respectively, of anexemplary coupling ring of the apparatus of FIG. 2A.

FIGS. 2G and 2H are top and perspective views, respectively, of anexemplary positioning ring of the apparatus of FIG. 2A.

FIG. 2I is a perspective view of a fastener of the apparatus of FIG. 2A.

FIG. 3 is a perspective view of exemplary coil windings positioned abovea mold for use in manufacture of an exemplary casting containing thecoil windings, in accordance with present invention.

FIG. 4 is a perspective view of an exemplary casting including coilwindings positioned above a casing to which the casting can be fixedlycoupled, in accordance with the present invention.

FIG. 5A is top view of an exemplary casing containing a casting withcoil windings, where the wall of the casing is spaced from the coilwindings, in accordance with the present invention.

FIG. 5B is a cross-sectional of the casing containing the casting ofFIG. 5A taken at line B-B.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1 is an exemplary embodiment of a TMS coil device 10, in accordancewith the present invention, including a casing 12 containing inductioncoil windings 15 of predetermined size and shape, an exemplaryembodiment of which is described in detail in the text accompanying thediscussion of FIGS. 2-4, and substantially fixed, with a high level ofprecision, at a predetermined location within and orientation inrelation to a bottom portion 14 of the casing 12. The casing 12 and aninterior region of the bottom portion 14 of the casing 12 have apredetermined size and shape, as discussed in detail below in the textaccompanying the discussion of FIGS. 4-5, such that the coil windings15, when installed within the bottom portion 14 of the casing 15, issubstantially precisely fixed at a predetermined location within andorientation in relation to the bottom portion 14 of the casing 12, andthus at a predetermined location and orientation in relation to a bottomouter surface 122 of the bottom portion 14 of the casing 12

FIGS. 2A and 2B illustrate exploded views of an exemplary apparatus 30for manufacture of the exemplary induction coil winding 15, inaccordance with the present invention. Referring to FIGS. 2A and 2B, andalso to FIG. 2C, which shows a partial view of the apparatus 30 duringan intermediate step in the manufacture of the coil winding 15, theapparatus 30 includes circularly-shaped guidance disks 16 and 18 havingplanar inner and outer surfaces 17A, 17B and 19A, 19B, respectively.Each of the disks 16, 18 includes an inner circumferential surface 21that defines a central, circular aperture 20 centered about a center Cof the disks 16, 18. Further referring to FIG. 2D, which shows a planview of the disk 18, the surface 21 of each of the disks 16,18 is at anominal radial distance R from the center C and includes arectangularly-shaped notch 22 extending a maximum of a radial distanceR8 away from the center C of the disks 16, 18.

Referring to FIGS. 2B, 2C and 2D, the disk 18 defines four apertures 26,which extend radially between a distance R1 and a distance R2 from thecenter C of the disk 18. Each of the apertures 26 is spaced about 90°from an adjacent aperture 26 and has a circumferential width W, exceptat rounded, opposing radial ends 27A and 27B. The radial end 27B extendsinwardly toward the center C of the disk 18 starting from a radialdistance R4 from the center C. The radial end 27A extends outwardly fromthe center C of the disk 18 starting from a radial distance R5 from thecenter C. In addition, the disk 18 defines an aperture 25 extendingcircumferentially between two of the apertures 26 and a radial distanceof between R7 and R6 from the center C, where R7 is between R and R4 andR6 is slightly larger than R4.

Referring again to FIG. 2A and also to FIG. 2E, which is a top view of acircularly shaped coupling ring 33 which is part of the apparatus 30used in the manufacture of the coil winding 15, and FIG. 2F, which isperspective view of the coupling ring 33, the coupling ring 33 includesan outer portion 34 encircling a portion of an outer circumferentialsurface 39 of a positioning ring connection portion 36. The outerportion 34 has a circumferential outer surface 35 at a radial distanceR3 from a center C of the coupling ring 33 and a circumferential innersurface 37 at a radial distance R8 from the center C of the ring 33. Theconnection portion 36 includes an inner circumferential surface 41defining an aperture 45 with a notch 46. The aperture 45 with the notch46 has the same configuration and dimensions as the aperture 20 with thenotch 22 of the disk 18. The portion of the surface 39 not encircled bythe outer portion 34 includes three rectangularly shaped projections 43having a maximum radial distance R3 from the center C and spaced about90 degrees from each other. The notch 39 is spaced about 90 degrees froman adjacent projection 43.

Referring to FIG. 2A and to FIGS. 2G and 2H, which show plan andperspective views, respectively, of a circularly-shaped positioning ring50 of the apparatus 30 used in the manufacture of the coil winding 15,the ring 50 includes inner and outer circumferential surfaces 52 and 54,respectively, and an inner circumferential surface 56. The inner surface52 defines an aperture region 57 centered at a center C of the ring 50,is at a radial distance R3 from the center C of the ring 50 and has thesame axial thickness as the surface 35 of the coupler ring 33. The innersurface 56 is at a nominal radial distance R8 from the center C anddefines three apertures 58 having the same size and configuration, andpositioned along the surface 56 in relation to one another in the samemanner, as the projections 43 of the coupler ring 33. In addition, theouter surface 54 is at a nominal radial distance R4 from the center C,has an axial thickness T1 and defines four apertures 59. The apertures59 extend radially toward the center C, are the same size and shape asthe radial ends 27B of the ring 18 and have an axial thickness T2 thatis less than the thickness T1.

Referring to FIGS. 2A-2H, the apparatus 30 is used to manufacture thecoil winding 15, in accordance with the present invention, by insertingan end portion 60 of a flat copper wire 62, from the side 19A of thedisk 18, through the aperture 25. The end portion 60 is then bentagainst the surface 19B of the disk 18, which secures the wire 62 forwinding about the circumferential surface 54 of the ring 50 as describedbelow. After the wire 62 is secured to the disk 18, the wire 62 is woundat least about one revolution around the surface 54. Then, after thecenter C of the ring 50 is aligned with the center C of the couplingring 33 and the protrusions 43 are aligned with the apertures 58, thecoupling ring 33 is inserted into the aperture 57, such that theprotrusions 43 are received within the correspondingly aligned apertures58, thereby mating the ring 50 to the coupling ring 33. Then, after thecenter C of the aperture 20 of the disk 16 is aligned with the centers Cof the combination of the rings 33 and 50 and the center C of theaperture 20 of the disk 18, with the radial ends 27B of the disk 18axially aligned with the apertures 59 in the ring 50, the surface 17A ofthe disk 16 is moved into contact with and forced against the outerradial surface of the ring 50 opposite the apertures 59, and the surface19A of the disk 18 is moved into contact with and forced against theouter radial surface of the ring 50 defining the apertures 59. In theresulting combination, the disks 16 and 18 are aligned with each otherand the ring 50 is disposed between the disks 16 and 18 and in aspecific alignment with the disk 18.

While this aligned combination is maintained, a conventional, rotatableaxle (not shown) having an outer circumferential surface with a notch ofthe same size and configuration as the aperture 20 with the notch 22 isinserted, threaded end first, through the aligned combination, such thatthe threaded end extends from the radial surface 19B. A securing means70, such as a nut and bolt, is screwed onto the threaded end of the axleto fixedly secure the combination so that the disks 16 and 18 and thering 50 cannot move axially relative to each other. The axle is thenrotated, which causes the disks 16 and 18 with the ring 50 to rotateabout the respective centers C. During rotation of the axle, the disks16 and 18 accurately and precisely guide the wire 62 onto the surface 54of the ring 50 as the wire 62 winds around the surface 54 and forms thecoil winding 15 having a desired, predetermined axial and radialdimension. The number of times that the wire 62 is wound around the ring50 is subject to the limitation that the outer surface of the outermostwinding of the wire 62 does not exceed a radial distance R5 from thecenter C. Therefore, the coil winding 15 does not cover a portion of theaperture 26 at the radial distance of at least R5 from the center C,thereby providing that the coil winding 15 does not cover at least theend portion 27A at the furthest most radially extending portion of theaperture 26. In a preferred embodiment, the disks 16 and 18 are securedto the ring 50 and the ring 50 is precisely sized so that the dimensiontolerance of the coil winding 15 in the direction axial to the windingof the wire 62 is within 0.2 mm of a predetermined, expected value, orat least within 1 mm of a predetermined, expected value, and further theaxle is controllably rotated so that the radial dimension of the coilwinding is within about 0.2 mm of a predetermined, expected value, or atleast within about 1 mm of a predetermined, expected value.

After the wire 62 is wound around the ring 32 a desired number of times,a latch or fastener 80 is inserted into one of the apertures 26.Referring to FIG. 2I, which shows a perspective view of an exemplaryfastener 80, which is preferably made of plastic, the fastener 80includes ends 80A, 80B extending orthogonally from an interconnectingmember 84 and including inner surfaces 86A, 86B, respectively, facingeach other. The member 84 is fixed or adjustable in length, such thatthe distance between the inner surfaces 86A and 86 is fixed oradjustable in length. The end 80B is inserted through the end portion27B of the aperture 26, and the end 80A is inserted through the portionof the aperture 26 not covered by the coil winding 15, which uncoveredportion at least includes the end portion 27A. When the ends 80A, 80B ofthe fastener 80 are installed within the aperture 26, the end 86A facesand contacts the outermost winding of the coil winding 15 and the end86B faces and contacts the innermost winding of the coil winding. Thelatch 52 is of a fixed length, or adjusted to a obtain a desired length,providing that the ends 86A, 86B force the outermost and innermostwindings of the coil winding 15 toward each other so as to maintain afirm and tight winding of the wire 62, which substantially fixes thesize and shape of the coil winding 15. Preferably, several latches 80are installed in respective apertures 26 to fix the size and shape ofthe coil winding 15. After the latches 80 are installed, the securingmeans 70 is removed from the axle and the coil winding 15 wound aroundthe ring 50 and including the attaches latches is separated from thecoupling ring 33 and the disks 16 and 18. Advantageously, the ring 50and the latches 80 of the apparatus 30, along with the disks 16 and 18,provide that the coil winding 15 manufactured by the apparatus 30 has adesired, predetermined shape and size, and that such manufactureprovides a very high level of precision and is readily repeatable.

In the illustrated preferred embodiment, the latches 80 extend over onlyone radial surface or side of the coil winding 15. Consequently, theother side of the coil winding 15 can be positioned as close as possibleto the outer surface 122 of the bottom portion 14 of the casing 12,which would be placed adjacent to or in contact with the head of asubject during operation of the TMS coil device 10. By placing the coilwinding 15 in the casing 12 as close as possible to the surface 122, thestimulating power that will reach the subject's head is maximized.

In a further embodiment of the present invention, the manufacture of aninduction coil winding for inclusion in the casing 12 of the TMS coildevice 10 also includes encasing coil windings in a casting. Referringto FIG. 3, a mold 90 defining a casting region 92, and preferablyincluding two alignment portions 94, is provided. In the illustratedembodiment, the casting region 92 is shaped to receive two inductioncoil windings 15, where each of the alignment portions 94 has a size andshape corresponding to the size and shape of the aperture 57 of the ring50, and where each of the windings 15 is preferably manufactured asdescribed above with a copper wire 62 wound around the positioning ring50 and fixed in size and shape by latches 80. The manufacture of asingle, integral casting 100 including the windings 15 is performed bydisposing the rings 50 of the windings 15 adjacent to each other, withthe apertures 57 respectively aligned with the portions 94, and thensliding the rings 50 over the respective portions 94 into the castingregion 92. The portions 94 substantially fix the rings 50 and, thus eachof the coil windings 15, in a predetermined location and orientation inrelation to each other. After the coil windings 15 are fixedlypositioned within the casting region 92, the casting region 92 is filledwith casting material. When the casting material hardens, the casting100 containing the two coil windings 15 wound around the respectiverings 32 has been formed and is removed from the mold 90. The casting100 ensures that the two coil windings 15 remain fixed in location andorientation in relation to each other, as provided by the portions 94.

In a further embodiment of the present invention, the manufacture of theTMS coil device includes coupling a pair of induction coil windingsencased within a casting at a predetermined location within andorientation in relation to a casing having a predetermined size andshape. Referring to FIG. 4, the exemplary bottom portion 14 of thecasing 12 of the TMS coil device 10 includes a side wall 110 and abottom wall 112 defining a casting receiving region 114. The castingreceiving region 114 has a predetermined size and shape and includes apair of circularly-shaped protrusions 116 extending upwardly from thebottom wall 112. Each of the protrusions 116 has an outer diameter andheight substantially equal to the inner diameter and axial thickness ofthe aperture 57 of the ring 50. Each of the protrusion 116 can receiveand fixedly mate with the ring 50 of an induction coil winding 15,preferably which is substantially the same as the induction coil winding15 with the fastener 80 and the ring 50 manufactured as described above,and most preferably, with the rings 50 of a casting 100 containing apair of the coil windings 15 each with the fasteners 80 and the ring 50manufactured as described above.

In one embodiment, the casting 100 containing the two coil windings 15wound around the respective rings 50 is inserted into the region 114 byaligning the apertures 57 with the respective protrusions 116 and thensliding the rings 50 over the protrusions 116 until bottom surface 101of the casting 100 contacts the opposing surface of the bottom wall 112.The protrusions 116, and optionally the side wall 110, with a high levelof precision, fix the positioning rings 50, and thus the coil windings15 contained in the casting 100, at a predetermined location within andorientation in relation to the bottom portion 14 of the casing 12. Thecasing 12 is closed by placing a top part covering (not shown) over thebottom portion 14. The top part covering has protrusions (not shown)opposite portions of the region 114 that, during installation of thecasting 100 in the casing 12, force the positioning rings 50 firmly overthe protrusions 116, such that the bottom surface 101 of the casting 100contacts the opposing surface of the bottom wall 112 of the portion 14.

Thus, the bottom portion 14, and the positioning rings 50 around whichthe respective coil windings 15 are wound, accurately position the coilwindings 15 in the direction axial to the coil windings 15, andpreferably within about 0.1 mm of the expected location of the coilwindings 15 in the bottom portion 14. In a further embodiment, theregion 112 and the protrusions 116 are of a size and shape ensuring thatthe coil windings 15 or the casting material forming the casting 100 donot contact the wall 110 of the casing 12, and thus cause errors in thepositioning of the coil windings 15 within the TMS coil device 10.

Advantageously, in accordance with the present invention, a coil windingcan be manufactured precisely and repeatability to have a predeterminedsize and shape, and a coil winding can be positioned within a casing ofa TMS coil device at a predetermined location and orientation inrelation to another coil winding and the casing precisely andrepeatably, where the casing has a predetermined Size and shape, suchthat information representative of the predetermined size and shape ofthe coil windings, and the location and orientation of the coil windingsin relation to each other and the casing of the TMS coil device can beused to perform NBS with a high level of accuracy.

In a further preferred embodiment, the casting receiving region 114 isslightly larger in size than the casting 100 received and fixedlycoupled within the casting region 114 of the casing 12. Referring toFIG. 4, and to FIG. 5A, which is a top view of an exemplary embodimentof the bottom portion 14 of the casing 12 including the casting 100fixed within the region 114, and to FIG. 5B, which is cross-sectionalview of the bottom portion 14 of FIG. 5A taken along cross-sectionalline B-B, in accordance with the present invention, the casting region114 is of a size and shape that a space 120 is defined between thebottom wall 112 and the side wall 110 and the portions of the casting100 facing the walls 110 and 112. In a preferred embodiment, the side ofthe coil windings 15 opposite the side including the fasteners 80constitutes the surface of the casting 100 facing the bottom wall 112and defines the space 120 at least in part.

During manufacture of the casing 12, the bottom portion 14 is sealedwith a gas contained in the space 120. The gas has a thermalconductivity lower than that of the coil windings 15 and the materialfrom which the casing 12 is formed, so as to reduce the rate of transferof heat energy from the coil windings 15 to the casing 12 duringoperation of the TMS coil, and where the thermal conductivity is not solow as to insulate the coil windings too much and cause the coilwindings 15 to exceed a predetermined temperature too quickly duringcontinuous or substantially continuous operation of the TMS coil device10. The gas in the space 120 is preferably air. The thickness of thespace 120, said thickness being the dimension extending between thebottom surface of the coil winding to the bottom wall of the casing,should not be greater than about 2 mm.

During operation of the TMS coil device 10, heat energy generated in thecoil windings 15 radiates through the spacing 120 to the adjoiningportions of the walls 110 and 112 of the casing 12. The transfer of asubstantial amount of the heat energy generated at the coil winding 15by radiation through the space 120, instead of by conduction through thecasing material as existing in some prior art TMS coil devices, reducesthe rate of transfer of the heat energy generated in the copper wire 62of the coil windings 15 to the outer surface 122 of the casing 12 duringoperation of the TMS coil device 10. Although conduction of heat energyfrom the coil windings 15 to other portions of the casing 12 occursthrough the positioning rings 50 and the casting material of the casting100 surrounding the positioning rings 50, the spacing 120 substantiallyreduces the rate of transfer of heat energy to the surface 122 because asubstantial portion of the heat energy generated at the coil windings15, which otherwise would be transferred to the surface 122 from thefacing surface of the coil windings 15, is instead radiated through thespacing 120. The spacing 120 with the gas causes heat energy toconcentrate in the copper coil windings 15 and the casting material 100,thereby slowing transfer of the heat energy to the surface 122.

The spacing 120 in the TMS coil device 10, thus, reduces the rate atwhich heat energy from the coil windings 15 transfers to the surface122, such that it takes a longer time period for the temperature of theouter surface 122 of the casing 12 to rise above a predetermined safetylevel. Consequently, a greater number of TMS pulses can be sequentiallyapplied using the inventive device 10 before the temperature of theouter surface 122 exceed the predetermined safety level. For example,the advantages of the TMS coil device 10 with the spacing 120 areevident when its operability is compared to the operability of asimilarly constructed TMS coil device which (i) does not have a spacecontaining a gas, such as air, between a coil winding and the casing, or(ii) does not include a casting which encloses a coil winding and isseparated from the casing by a spacing containing a gas, such as air.The TMS coil device 10 in accordance with the present invention cansequentially apply approximately double the number of TMS pulses thanthe comparable TMS coil devices without the spacing can apply before anunsafe temperature is reached at the outer surface of the TMS coildevice 10.

As well known in the art, the temperature of a coil winding depends onthe heating power, or the resistive losses in the copper wiring thatforms the coil windings, and the mass and heat capacity of the materialsurrounding the copper wiring that absorbs the heat generated at thecoil windings. In a further embodiment, referring to FIG. 1, a top wall125 of the casing 12, which covers the side of the coil windings 15opposite the bottom wall 122 of the casing 12, includes a phasetransition material having a low conductivity, such as about 0.1-0.2W/m*K, which transforms its phase from solid to liquid when heated,thereby increasing the heat capacity of the TMS coil device 10. In afurther embodiment, the phase transition material is mixed with abinding material, so that the phase transition material changes itsphase within the binding material, but the binding material remainssolid. In another embodiment, the top wall 125 is formed from a materialhaving good heat conductivity and electrical insulation properties, suchas a ceramic solid structure or a powder of such material, to improvethe transfer of heat energy from the coil windings 15 to the phasetransition material in the top wall 125 of the casing 12.

Although preferred embodiments of the present invention have beendescribed and illustrated, it will be apparent to those skilled in theart that various modifications may be made without departing from theprinciples of the invention.

1. A transcranial magnetic stimulation induction coil device comprising:at least one coil winding having a predetermined thickness and inner andouter surfaces at predetermined first and second radial lengths,respectively, from a center of the coil winding, wherein the firstsurface defines an aperture, a fastener extending from the inner surfaceof the coil winding to the outer surface of the coil winding, whereinthe fastener couples the inner surface of the coil winding to the outersurface of the coil winding such that the coil winding has apredetermined size and shape, and a ring having an outer surface at aradial length from a center of the ring substantially equal to the firstradial length, wherein the ring is positioned within the aperture of thecoil winding such that the outer surface of the ring is in contact withthe inner surface of the coil winding.
 2. The device of claim 1, whereinthe fastener includes a plastic material.
 3. The device of claim 1,wherein the outer surface of the ring defines at least one notchextending radially toward the center of the ring, wherein the fastenerhas first and second ends, where the first end of the fastener iscoupled to the inner surface of the coil winding at the notch and thesecond end of the fastener is coupled to the outer surface of the coilwinding.
 4. The device of claim 1 further comprising: a casting of apredetermined size and shape encasing the coil winding at apredetermined location within, and orientation in relation to, thecasting.
 5. The device of claim 4 further comprising: a casing having apredetermined size and shape and including a bottom wall and a sidewall, wherein the bottom and side walls define a receiving region havinga predetermined size and shape, wherein the casting is coupled to, andpositioned at a predetermined location within and orientation inrelation to, the receiving region.
 6. The device of claim 5, wherein thebottom wall of the casing includes a projection extending into thereceiving region at a predetermined location on the bottom wall, whereinthe projection has a predetermined size and shape, wherein the castingdefines an aperture at a predetermined location and having apredetermined size and shape matched to the predetermined size and shapeof the projection in the casing, wherein the projection of the casing ismated to the aperture of the casting such that the coil winding withinthe casing is at a predetermined location within and orientation inrelation to the casing.
 7. The device of claim 6, wherein the castingincludes a bottom outer surface facing the bottom wall of the casing,wherein at least a portion of the bottom wall of the casing and at leasta portion of the bottom outer surface of the casting define a spacethere between, and wherein the space includes a gas.
 8. The device ofclaim 7, wherein the gas includes air.
 9. The device of claim 7, whereinthe coil winding has a bottom surface facing the bottom wall of thecasing and constituting a portion of the bottom outer surface of thecasing, wherein the bottom surface of the coil winding defines a portionof the space, wherein the space has a thickness dimension extendingbetween the bottom surface of the coil winding and the bottom wall ofcasing, and wherein the thickness dimension is not greater than about 2mm.
 10. The device of claim 7, wherein the casing includes a top walloverlying a side of the coil winding opposite to the bottom wall of thecasing, and wherein the top wall includes a phase transition materialhaving a heat conductivity substantially lower than the conductivity ofceramic.
 11. The device of claim 1 further comprising: a casing having apredetermined size and shape and including a bottom wall and a sidewall, wherein the bottom and side walls define a receiving region havinga predetermined size and shape, wherein the coil winding is coupled to,and positioned at a predetermined location within and orientation inrelation to, the receiving region.
 12. The device of claim 11, whereinthe coil winding includes a bottom outer surface facing the bottom wallof the casing, wherein at least a portion of the bottom outer surface ofthe coil winding and at least a portion of the bottom outer surface ofthe casing define a space there between, and wherein the space includesa gas.
 13. The device of claim 1 further comprising; at least oneadditional coil winding having a predetermined thickness and inner andouter surfaces at predetermined first and second radial lengthssubstantially equal to the those of the first coil, respectively, from acenter of the coil winding, wherein the first surface defines anaperture, a fastener extending from the inner surface of the coilwinding to the outer surface of the coil winding, wherein the fastenercouples the inner surface of the coil winding to the outer surface ofthe coil winding such that the coil winding has a predetermined size andshape, and a ring having an outer surface at a radial length from acenter of the ring substantially equal to the first radial length,wherein the ring is positioned within the aperture of the coil windingsuch that the outer surface of the ring is in contact with the innersurface of the coil winding.
 14. The device of claim 13 furthercomprising: a casting of a predetermined size and shape encasing thecoil windings at a predetermined location within, and orientation inrelation to, the casting.
 15. The device of claim 13, wherein thefasteners are only on one side of the coil winding.